Reverse current protective system



July 1954 G. w. WEBER ETAL REVERSE CURRENT PROTECTIVE SYSTEM 2 Sheets-Sheet 2 Filed July 31, 1953 Generator J a/Z'a 6 3% Q O 0 6 N wk): m d wm i/w aa .r aw w a r Patented July 13, 1954 UNITED STATES PATENT OFFICE REVERSE CURRENT PROTECTIVE SYSTEM Gay W. Weber, Erie, and Richard K. Gerlitz, Northeast, Pa., assignors to General Electric Company, a corporation of New York 1953, Serial No. 371,628

Application July 31,

13 Claims. 1

This invention relates to a reverse current protective system for protecting a direct current load, including a battery, against connecting the source to the load when the source voltage is less than the voltage of the load and for disconnecting the source from the load when the load current reverses and flows from the load into the source.

In many applications, it is possible for the prime mover of a generator to run at any speed from maximum speed to zero speed. Such an application might be the axle of a railway passenger car; therefore, there are many occasions when such a prime mover is not running at a sufficient speed to cause the generator to produce the needed voltage.

An object of this invention is to provide a simple and reliable reverse polarity protective system that will prevent the connection of the source to the load until it is producing a suificient voltage of proper polarity.

Another object is to provide a potential network that will cause a rapid current increase in a selected portion of a protective system when the voltage of the source exceeds a predetermned value.

A further object is to provide a battery charging system whereby the connecting switch will not tend to pump or oscillate when closed or opened.

In accordance with one form of this invention, a source of direct current is serially connected to an impedance and a relay having a plurality of windings. The contacts of the relay are arranged to connect the battery in a series relation with one of the relay coils when the relay is energized. A unidirectional conducting means is arranged to connect the battery in a series relation with both relay coils. As the voltage of the source increases the current in the relay coils increases until the voltage across the impedance exceeds the voltage of the battery. At this point the unidrectional conducting means will start to conduct current from the Winding of the relay to the battery. This will effectively lower the impedance in series with the relay coils. A small further increase in the voltage of the source will cause the relay contacts to close. Should the source be operated so as to produce a reversed voltage the unidirectional means will not conduct current, thus preventing reduction of the impedance in series with the relay coils.

When the relay contacts close, the unidirectional conducting means ceases to conduct cur rent, effectively increasing the impedanc in series with the two relay coils. The current through the series impedance alone is just sufficient to hold the relay contacts closed. The series coil of the relay which is connected in series with the relay contacts and the battery is so wound that the current flowing from the source to the battery aids the current flowing in the impedance. Reverse current in the series coil decreases the net excitation of the relay, causing its contacts to open.

This invention will be better understood and other objects and advantages appreciated by referring to the following detailed specification taken in conjunction with the accompanying drawings in which:

Fig. l is a schematic circuit diagram of the simplest embodiment of this invention;

Fig. 2 is an explanatory voltage ampere turn curve used with Fig. 1;

Fig. 3 illustrates another embodiment of this invention;

Fig. 4 illustrates another embodiment of this invention;

Fig. 5 is an explanatory voltage ampere curve used with Fig. 4;

Fig. 6 illustrates another embodiment of this invention.

Referring to Fig. l, i represents a suitable source of direct current, such as the generator, which is arranged to be connected to the load system represented by the battery 2 having a positive terminal and a negative terminal by means of a suitable contact 3. Before the contact 3 is closed, the current from the source I passes through the electromagnetic operators shown as coils 5 and t of relay Q, junction 7 and through an impedance shown as resistor 8. As the voltage of the source l increases, current through the coils i and 5 and the resistor 8 increases. The magnitude of voltage across resistor 8 is determined primarily by the source voltage. At the point where the voltage across resistor 8 becomes greater than the battery voltage, rectifier i2 will start to conduct. This eiiectively reduces the resistance in series with the windings 5 and 6 of the relay 4. A further increase in voltage will cause a substantial increase in current through rectifier l2 and through the coils 5 and E.

This is more clearly shown by Fig. 2 which is a plot of the ampere turns of the relay coils on the vertical axis against the generator voltage on the horizontal axis with the contact 3 open. The vertical dotted line of Fig. 2 represents the fixed voltage of the battery 2 and is shown as a line extending from some point on the generator voltage axis. The ampere turns through the coil windings are represented by the solid black curves of the drawing. Line l3 represents the line the ampere turns will follow when resistor 8 is the only effective resistance in series with the source l and the coils 5 and 6. At some point is the current will start to flow through the rectifier 52 into the battery 2 and the slope of the ampere turn curve will be increased. As soon as the ampere turns curve reaches the relay energization setting shown as the horizontal dotted line it, the relay i is adjusted to close contact 3. This is shown at point it on the curve. Assuming the impedance of the circuit of the battery 2, the coils 5 and 6 and the rectifier i2 is linear, the line is will be a straight line, the slope of which depends on this impedance in parallel with resistor '8. Since the horizontal position of the steep portion of the curve 55 is deteunined by the existing battery voltage, a differential action is obtained similar to that usually provided by a differential coil. Ehis causes the difierence be tween the generator voltage and the battery at the relay pickup point to vary only slightly over a wide range of battery voltages. Hence, a wide degree of accuracy on pickup is inherent in the system.

When the relay fl picks up, the voltage from the line 253 which is connected to the current tap 2i between the two coils, is connected through contact to the positive terminal or the battery and load by line 22. Since the voltage of the source i is higher than the voltage of the battery 2, this causes a large surge of charging current to flow from the source to the battery through coil 5. ltaneously, rectifier i2 ceases to conduct and the ampere turns of coil 3 decrease to a value indicated by point 25 on line l3. A surge of charging current through the coil 5 prevents the relay from dropping out due to the sudden decrease in the ampere turns of coil 5; thus, the relay will not pump on closing. As long as the load current is flowing from the source, the series coil and the potential coil 3 are so wound as to aid each other in holding the relay l closed. When the source voltage drops below the cattery voltage and reverse current flows from the battery through series coil ii to the source i, the reverse ampere turns or series coil S cancel some of the potential coil 5 ampere turns, lowering the net excitation of the relay. When the net ampere turn level is decreased to the cleenergization point of the relay represented by the horizontal dotted line 23 of Fig. 2, the relay drops out, opening contact 3. At this point the source voltage is less than the battery voltage and the relay cannot reclose. This condition prevents the relay from pumping on deenergization.

Should the source 3 be operated to produce a reverse voltage, the rectifier 52 would not conduct at any time. ihe result would be, as shown in Fig. 2, that the ampere turn line would follow line 52 without having a steep portion as shown by Hi. The source is so arranged that it will not ordinarily produce a voltage great enough to energize the relay under these conditions. The slope of line it is inversely proportional to the resistance 3. If there is any danger of the relay energizing under reverse voltage, the resistance 8 may be increased until this danger is eliminated.

A further refinement is shown in Fig. 3 the adidtion of a potentiometer and shunt across battery 2 consisting of resistor 2 and resistor ill. The rectifier i2 is connected to voltage tap shown as point which is the junction between these two resistors. Since the voltage of point H is less than the full battery voltage, it is obvious that rectifier 22 will begin to conduct when point i is less than full battery voltage. Referring to Fig. 2, this means that point moves to the left on curve 13. By proper choice the resistors Hi and 24; can be so proportioned tha rectifier 52 will begin to conduct when the source voltage is exactly equal to the battery voltage. This results in a decreased differential between source voltage and battery voltage at the "chap point of relay :3.

jhis refinement is of par ticular interest where a high resistance potential co must be used with a consequent high voltage differential at the energizing point.

A still further refinement is shown in Fig. by the addition of a rectifier s between the resistor 2 and the point ii. Resistor 2% may be negligible so that the voltage drop between the tap ii and line 22 is due entirely to the impedance of the rectifier El.

Resistors s and it are so proportioned that rectifier will be conducting at all times until after the value of ampere turns in coil 5 is reached. Therefore, under normal operating conditions, rectifier s has no effect on the operation of the system However, if the contacts should fail to close, a d the voltage of the source i should rise to a value which xceeds the voltage of the battery 2 by a large amount, rectifier Q will cease to conduct and effectively increase the impedance in series with cell Referring to Fig. 5, the rectifier e ceases to conduct at point l5 and the ampere turns of coil 5 increase along the line we as the voltage or" the souce increases further. Thus, in a circuit where a separately operated protective device might prevent the closure of contacts 3, the rectifier s would serve to protect coil 5 from over-current.

Fig. 6 shows a modification of Fig. l with a heavy duty contact 2'? added. The contact 3 is connected in the circuit to activate the high impedance coil 28 of relay 2Q cau g contact 2'! to close. Referring to Fig. 1, sho the current through contact 3 be very large when the dropout occurs, arcing or" these contacts would cause a gradual erosion of the contact material, thus lessening the contact pressure. This decrease in the contact pressure would cause the dropout point as shown by line 23- of Fig. 2 to be lowered slightly. The additional relay 2?? is used to prevent this occurrence and allow sensit' ity of the system to continue in heavy duty applications.

It is easily seen that this system results in a reverse current battery char ing system that will not tend to pump either on he pi sup operation or the dropout operation.

While we have shown and described a particular embodiment of this invention, further modifications and improvements will occur to it to those skilled in the art. We desire be understood, therefore, that this i; v limited to the form shown and we intend the appended claims to cover all nod aticns which do not depart from the spirit scope or this invention.

What we claim as new and to se ure by Letters Patent of the United States i":

l. A battery charging system comprising a source or" current, an electronragnetleally operable switch, two coils capable of actuating salt or itch,

npedance, one of said coils and said imp ance being serially connected across said source, a battery, and means positioned between said battery and the junction of said coil and said impedance to provide a current path only when the voltage of said junction is greater than the voltage of said battery whereby the impedance in series with said coils and said source is reduced.

2. A battery charging system comprising a source of current, an eleotromagnetically operable switch, contacts operated by said switch, two coils capable of actuating said switch, an impedance, one of said coils and said impedance being serially connected across said source, a battery, he other of said coils, said battery and said contacts serially connected across said source, and means positioned between said battery and the junction of said coil and said impedance to provide a current path only when the voltage of said junction is greater than the voltage of said battery whereby the impedance in series with said coils and said source is reduced.

3. A reverse current protective system comprising a source of current, an electromagnetically operable switch, contacts operated by said switch, two coils capable of actuating said switch, an impedance, one of said coils and said impedance being serially connected across said source, a battery, the other of said coils, said battery and said contacts being serially connected across the said source, coils connected to produce opposing flux when current is flowing from said battery to said source, and means positioned between said battery and the junction of said coil and said impedance to provide a ciu'rent path only when the voltage of said junction is greater than the voltage of said battery whereby the impedance in series with said coils and said source is reduced.

4. A battery charging system comprising, a source or current, an electromagnetically operable switch, two coils capable of actuating said switch, an impedance, said coils and said impedance being serially connected across said source, a battery, a potentiometer connected across said battery, said potentiometer having a voltage tap, and means positioned between said tap and the junction of said coil and said impedance to provide a current path only when the voltage of said junction is greater than the voltage of said tap whereby the impedance in series with said coils and said source is reduced.

5. A battery charging system comprising an electromagnetic source of direct current, a relay having two serially connected actuating coils, a resistance, said coils and said resistance serially connected across said source, a battery, a potentiometer having a voltage tap thereon and being connected across said batter and unidirectional conductor means positioned between said tap and the junction of said coils and said resistance to reduce the impedance of said series circuit by providing a second current path between said coils and source only when the voltage of said junction is greater than the voltage of said tap.

6. A battery charging system comprising an electromagnetic source of direct current, a relay having two serially connected coils with a current tap therebetween, an impedance, said coils and said impedance serially connected across said source, a battery, a unidirectional potentiometer connected across said battery, said potentiometer having a voltage tap thereon, switch means having a pair of terminals short circuited in response to current in said relay coils, one of said terminals connected to said current tap and the other of said terminals connected to said battery so that said battery may be connected across said source for charging from said source, and means for connecting said voltage tap to the junction between said coils and said resistance when the voltage of said junction is greater than the voltage of said voltage tap whereby the impedance in series with said coils and said source is effectively reduced.

'7. A battery charging system comprising an electromatic source of direct current, two serially connected coils with a current tap therebetween, a first resistance, said coils and said first resistance serially connected across said source, a battery, a switch having a pair of terminals short circuited in response to current in said coils to serially connect said battery and one of said coils across said source, a unidirectional conductor means, a voltage tap, a second resistance, said unidirectional means, said voltage tap, and said second resistance being serially connected across said battery, and mean positioned between said voltage tap and the junction of said coils and said resistance to provide a current path only when the voltage of said junction is greater than the voltage or" said voltage tap whereby the impedance in series with said coils is reduced.

8. A battery charging system conipri g a variable voltage electromagnetic source of direct current, two serially connected coils, a current tap between said coils, a first resistance, said coils and said first resistance serially connected across said source, a battery, switch means having a pair of terminals short circuited. in response to current in said coils, one or said terminals electrically connected to said current tap and the other of said terminals connected to said battery, so that said battery and one of said coils may be serially connected across source for charging, a rectifier means, a voltage tap, a second resistance, said rectifier, voltage tap and said second resistance being serially connected across said battery, and another rectifier positioned between said voltage tap and the junction of said coils and said first resistance to provide a current path therebetween only when the voltage of said junction is greater than the voltage of said voltage tap whereby the impedance in series with said coils is reduced.

9. A battery charging system comprising a source of direct current, two serially connected coils with a current tap therebetween, a first impedance, said coils and said impedance ser' ll connected across said source, a battery having two terminals, an electromagnetically operable switch means having a pair of terminals short circuited in response to current in said coils, one of said switch terminals electrically connec ed to said current tap and the other of said switch terminals electrically connected to one of said battery terminals so that when said switch means is short circuited said battery will be connected a"- cross said source in series with one of said coils, a rectifier means, a voltage tap, a second impedance, a third impedance, said rectifier means, said voltage tap, said second impedance and said third impedance serially connected across said battery, said rectifier means connected to conduct current from one of said battery terminals toward the other of said battery terminals only when the voltage across said battery exceeds the voltage across said third impedance, another rectifier connected between said voltage tap and junction of said coils and said first impedance to reduce the impedance of the series circuit of said coils by providing a second current path between said junction and said source only when the voltage of said junction is greater than the voltage across said third impedance.

10. A battery charging system comprising a source of direct current, a first relay having a series coil and a potential coil serially connected, a current tap between said coils, a first impedance, coils and said first impedance being serially connected across said source, a second relay having a high impedance coil, a first switch means having a pair of terminals short circuited in response to energization of said first relay, one of said terminal connected to said current tap and the other of said terminals connected to said high impedance coil for connecting said high impedance coil across said source in response to short circuit of said terminals, a battery having two terminals, a second switch means having a pair of terminals short circuited in response to the energization of said second relay, one of said terminals of said second switch means connected to said current tap and the other of said terminals of said second switch means connected to one of said battery terminals for se ially connecting said battery and said series coil acros said source in response to short circuit of said terminals of said second switch means, a unidirectional potentiometer means having a voltage tap thereon, said potentiometer connected across the terminals of said battery to conduct battery current only when the voltage of said battery exceeds the voltage of tap, and unidirectional conductor means positioned between said voltage tap and the junction of said coils and said first impedance to reduce the impedance of the series circuit or" said first relay coil by providing a second current path between said junction and source only when the voltage of said junction is greater than the voltage of said voltage tap.

11. A battery charging system comprising a source of direct current, two serially connected coils, an impedance, coils and said impedance serially connected across said source, a battery, a potentiometer connected across said battery, said potentiometer having a voltage tap thereon, a first unidirectional conductor means serially connected with said battery and said potentiometer for preventing charging of said battery from said voltage tap, a second unidirectional con doctor means positioned between tap and the junction of said coils and said impedance to provide a current path only when the voltage of said junction is of the same polarity and greater than the voltage of said voltage tap whereby the impedance in series with said coils is reduced.

12. A battery charging system comprising a source of direct current, a series coil, a potential coil, a current tap between said coils, an impedance, said coils and said impedance serially connected across said source, a battery, switch means having a pair of terminals operable in response to current in said coils, one of said terminals connected to said current tap and the other of said terminals connected to said battery so that said battery and said series coil may he serially connected across said source, said coils connected to produce aiding flux when current is flowing from said source through said coils opposing fiux when current is flowing from said battery through said source, a unidirectional potentiometer means connected across said battery, said potentiometer means having a voltage tap thereon, means positioned between said voltage tap and the junction of said coils and said impedance to reduce the impedance of said series circuit by providing a second current path between coils and said source only when the voltage of said junction is of the same polarity and greater than the voltage of said tap.

13. In combination, a source of direct current, a relay having a series winding and a potential winding, a first resistor in series with said windings, first unidirectional conducting means in parallel. with said first resistor, a load including a battery, other unidirectional conducting means shunting said batter a second resistor connected in series with both of conducting means to receive current from them when they are conductive, for preventing energization of relay until said first unidirectional conducting means is conductive, and means for preventing deenergization of said relay until said series coil carries a reverse current of a predetermined amount.

References Qiteel in the file of this patent UNITED STATES PATENTS Number Name Date 926,164 Bliss June 29, 1909 1,147,696 'Woodridge July 20, 1915 1,149,735 Creveling Aug. 18, 1915 1,298,46 Creveling Mar. 25, 1919 1,348,098 Eisenmann July 27, 1920 1,469,736 Sullivan Oct. 2, 1923 19252096 McNeil July 25, 1933 1,973,804 Frese Sept. 18, 1934: 1,993,0'70 Middleton Mar. 5, 1935 2381.420 Seeger et al Jan. 12, 1943 2,332,951 Thompson Oct. 26, 1%3 6%,313 Bell Aug. 5, 1952 FOREIGN PELENTS l umber Country Date 847,864 France July 10, 1939 

